Volvo 940 only blowing cold air
 

Hi - 1992 Volvo 940 GLE estate - non-turbocharged, no air conditioning, B230F engine. The air vents are only blowing cold air at the moment. Would be interested in suggestions to address this.

Caveat - the car has been sitting around unused since the start of the pandemic. I've run it up and down my driveway a few times, but it has been on SORN. I recently taxed, insured it and it scraped through its MOT. I've only used it for a couple of short local journeys however. It could just be the case that the stone cold engine really just hasn't had a chance to warm up?

The manual heater temperature control can be twisted between a third from cold, and fully hot. It cannot be twisted to the fully cold position. I remove the trim from under the steering column and i can see the cable moving the heater control valve. Prepared to replace the heater control valve if need be.

There is no coolant leak or coolant smell, so I'm assuming the heater matrix is ok.

Fans work as expected on all speed settings, so I assume the blower motor resistor is ok.

Would it be a good idea to remove the coolant hoses, and either replace or give them a thorough flush with a hosepipe (if I can get them off their fixtures without splitting the rubber)? There are two hoses going into the bulkhead from the engine block, followed by, I imagine, further hoses going to the heater control valve in the cabin. Is there anything else to think about here?

If I need to replace these hoses, will the Volvo take a relatively standard fit, or are they hard to come by?

Thanks!

Alternatively, I'm guessing, thermostat needs replacing?

If you have no leaks around the heater control valve I would leave that well alone :shocked:

As above. New heater control valves are virtually non existent.
The two hoses are shaped and difficult to source.
Q1. Is the temperature gauge working?
If it is, does it move to vertical (about halfway) after just a mile or so,
or does it loiter cooler than that?
Q2. Is the radiator top hose getting hot?
If it does, does it do this quite suddenly after idling the engine for a
while, or does it just warm up gradually?
If either or both of these apply then I would suspect the thermostat.
If you intend to replace the thermostat I suggest that you check whether you are able to loosen the nuts of the thermostat housing as they can be stubborn. If they are stubborn, give them a couple of doses of releasing fluid for a day or two before attempting to remove them. They should be flange nuts and the nut part is quite shallow.

That sounds like the trouble. Even once fully warm (temp gauge up to halfway/vertical point) it still takes time to thoroughly heat the matrix so takes a couple of miles before you get any real heat out of the heater. You should feel warmth after about 1/2-3/4 mile though but it won't win any prizes against a thermo-nuclear reaction at that point.

Also worth checking your viscous coupling on your cooling fan isn't siezed as that will increase warm up time.

I don't know if they're hard to come by, but be very careful getting them off - plenty of release oil and gentle wiggling, you don't want to crack the fittings. They go through the firewall and exit just to the left of the clutch pedal quite high up. Definitely don't mess with the HCV because replacements aren't available for RHD non-a/c cars.

I had this issue around this time last year and replacing the thermostat and giving it a good flush through sorted it. It's still not mega hot but it's pleasantly warm on a cold morning. I find it takes 20 minutes to get a good amount of heat out of the heater.

Just remember that the centre vents above the controls only deliver cold air - you only get warm air from the vents near the mirrors and from the floor vents.

You mention that the heater control can't be turned all the way cold, that's odd. It's just a simple mechanical connection to the HCV. Just wondering out loud if the HCV has worked loose slightly and rotated in its housing?

Ditto to all the above.
Re the heater control: As you are able to see the HCV you should be able to see where the wire core of the control cable is connected to the HCV lever by a clip. Release the clip and check whether you have full movement of the HCV lever and the heater control knob. Then move both to fully hot and reconnect the cable and check whether you have full movement hot to cold. If that doesn’t work disconnect them and move both to fully cold and check for movement. If this also fails then you will have to accept a compromise and reconnect appropriately.

Thanks all for your excellent advice.

I have concluded it is almost certainly the thermostat that needs replacing. The water temp needle did not reach 50% after the decent run I made last night. It hit about 30% where it 'loitered' for the remainder of the journey.

New Volvo original thermostat and gasket ordered. Will also drain, flush and replace the coolant.

HCV not turning to cold - I will remove the driver's side steering column trim and check whether it is correctly seated in its housing. Will also remove the clip and try the test Ian21401 suggests.

Glad I've managed to get the car running as it should again. It is a majestic, incredibly comfortable, glacially slow old bus and I adore it!

I'd replace the 'stat before going near the HCV if i were you. Before you start the drain, flush etc, ensure the heater is set to the hottest setting, it needs to be there so the matrix gets flushed too.

When you come to do it, invest in something like Comma X-stream Flush for the cooling system and add it as per the directions on it.

If it says run it at a fast idle for 20 minutes, take it for a half hour drive instead.

Once you're home and it has cooled somewhat, remove the 'stat housing and the old 'stat. Refit the housing then remove the top hose from the radiator stub. Use your garden hose in the open end of the top hose, if you have a Hozelock type fitting it should fit snugly inside the top hose.
Turn the water on for the hose and leave it running. This reverse flushes the system with the old stuff exiting via the radiator stub at the top. Usually takes about half hour to get it running clear, once it is running clear leave it 10 minutes or so more to ensure it really is clear.
Turn the hose off and remove it from the top hose. Remove the bottom hose from the bottom of the rad to drain off excess water from the rad and block and then refit - having a new Jublee clip for it is a wise move as they often rust.

Once the bottom hose is secure, add 5L of concentrated Ethylene Glycol antifreeze. The exact figure for 50/50 mix is something like 4.8L, can't recall it exactly and it's as close to 5L as makes very little difference.
Fit the new 'stat, note the seal sits around the edge of the 'stat ont on it or under it - there is a groove inside the seal to let it sit around the 'stat. Ensure the recess in the head and 'stat housing are clean and smooth, use some silicone grease in the groove and smear some on the outer parts of the seal too and fit, ensuring the jiggle valve is at the top if it has one.
Refit the 'stat housing and top hose to the rad.

Top up the expansion tank with fresh water (remember you already have enough antifreeze in so water is fine), refit the cap and squeeze the bottom hose several times to help move the air to the top. If the level drops in the tank, add more water to the "MIN" line and squeeze the bottom hose a few more times. Repeat until squeezing the bottom hose doesn't result in further drop of the level.

Refit the cap and take for a drive, ensuring you get it up to temperature and that the heater works, no leaks etc. Return home and park it facing uphill and leave to cool until the following day then check and top up the level to the "MIN" mark if needed.

I've used this method for decades on a variety of cars and it works. Whatever you do, don't be tempted to buy OAT coolant, doesn't matter how good the salesman says it is, it will destroy your engine.

If some idiot has previously used OAT coolant (usually red or orange) then you have other problems and could be the cause of your lack of heat. Hopefully they haven't though! :nah:

Agree, sounds like the stat. That's exactly what mine was doing before I replaced it. Mine is now up to temp within a mile/5 mins driving so unless you're in the Arctic its a stat issue. Having had diesels for many years I'm always surprised just how quickly a big old lump like the B200F warms up.

Easy job (just follow LairdScooby's guide above) - make sure you give the stat housing bolts and hose clips a really good soaking of WD40 the night before. You really don't want to strip those and they are a bit soft. The beauty of the 940 cooling system is that everything is so accessible, particularly on the 2l non-turbos. I'm a ham-fisted bodger and have done the stat and the radiator in the last year with no issues, not even skinned knuckles.